New research shows that blue eyes in people originated between 6,000 and 10,000 years ago with one single common ancestor.
Originally, it was boring, brown-eyed-only world out there for early humans, said Professor Hans Eiberg from the University of Copenhagen Department of Cellular and Molecular Medicine. Blue eyes started with a mutation that affected the OCA2 gene, the gene that controls the “P protein” that controls the melanin that give color to our eyes, hair and skin.
The mutation was not on the OCA2 gene directly, but rather on an adjacent, related gene. It created a switch that affected production of melanin in the iris of the eye. With this genetic “switch” set to off, melatonin is limited and brown eyes are “diluted” to blue.
So what about green or amber or other eye colors? They can also all be explained by differences in the amount of melanin the iris, and there’s considerable genetic diversity behind variations in brown eye color. But blue-eyed people show very little variation in the melanin in their eyes, and that’s all related to the one mutated gene.
“From this we can conclude that all blue-eyed individuals are linked to the same ancestor,” says Professor Eiberg. “They have all inherited the same switch at exactly the same spot in their DNA.”
Eiberg and his team studied the eyes and genes of people in Jordan, Denmark and Turkey as part of their research. Eiberg has been studying the topic since 1996, when he first concluded that the OCA2 gene was related to eye color.
Eye color is neither a beneficial or harmful mutation, Eiberg said. Instead “it simply shows that nature is constantly shuffling the human genome, creating a genetic cocktail of human chromosomes and trying out different changes as it does so.”